Pultrusion is a process for producing constant profile composites in continuous lengths. Composite articles made by the pultrusion process include I-beams, dowels, floor gratings, and the like. Pultrusion differs fundamentally from extrusion because a combined resin and fiber reinforcement is pulled rather than pushed through a die.
One pultrusion technique requires that a number of strands or rovings of fiber be pulled from continuous rolls through a reservoir of bonding resin to coat the fibers prior to their being shaped and cured. Examples are provided in U.S. Pat. Nos. 3,704,561, 3,983,668, 4,244,768, 4,289,563, and 4555,886. The evaporation of certain solvents from the reservoir, however, poses an environmental problem.
In an alternative technique, a fiber glass reinforcement is coated with resin and shaped around a mandrel in a heated die which cures the injected parts. While a number of articles having a variety of cross-sectional shapes may be fabricated by this method, the walls of these articles tend to be relatively thin and must sometimes be reinforced by lamination or winding with further fiber glass material.
Accordingly, an apparatus and method are needed for producing pultruded articles having substantially thick walls which can be produced in an efficient, convenient, and continuous operation.